EGFR Signaling Through an Akt-SREBP-1–Dependent, Rapamycin-Resistant Pathway Sensitizes Glioblastomas to Antilipogenic Therapy

Inhibitors of fatty acid signaling promote apoptosis in glioblastoma cells with highly active EGFR signaling. Inhibiting Lipid Metabolism to Combat Glioblastoma Glioblastoma, the most common form of brain cancer, is frequently lethal. Glioblastoma is often associated with increased signaling through the epidermal growth factor receptor (EGFR); however, therapeutic efforts focused on inhibiting EGFR signaling have been disappointing. Guo et al. analyzed tumor tissue removed from glioblastoma patients before and during treatment with the EGFR inhibitor lapatinib and found that EGFR signaling activated sterol regulatory element–binding protein 1 (SREBP-1), a key regulator of lipid metabolism, and increased the cellular concentrations of fatty acids. Intriguingly, inhibiting fatty acid synthesis promoted apoptosis in glioblastoma cells with substantial EGFR signaling both in vitro and when transplanted into immunodeficient mice, but not in glioblastoma cells with little EGFR signaling. Thus, inhibition of fatty acid synthesis may represent a new avenue toward treating glioblastomas driven by EGFR signaling. Glioblastoma, the most common malignant brain tumor, is among the most lethal and difficult cancers to treat. Although epidermal growth factor receptor (EGFR) mutations are frequent in glioblastoma, their clinical relevance is poorly understood. Studies of tumors from patients treated with the EGFR inhibitor lapatinib revealed that EGFR induces the cleavage and nuclear translocation of the master transcriptional regulator of fatty acid synthesis, sterol regulatory element–binding protein 1 (SREBP-1). This response was mediated by Akt; however, clinical data from rapamycin-treated patients showed that SREBP-1 activation was independent of the mammalian target of rapamycin complex 1, possibly explaining rapamycin’s poor efficacy in the treatment of such tumors. Glioblastomas without constitutively active EGFR signaling were resistant to inhibition of fatty acid synthesis, whereas introduction of a constitutively active mutant form of EGFR, EGFRvIII, sensitized tumor xenografts in mice to cell death, which was augmented by the hydroxymethylglutaryl coenzyme A reductase inhibitor atorvastatin. These results identify a previously undescribed EGFR-mediated prosurvival metabolic pathway and suggest new therapeutic approaches to treating EGFR-activated glioblastomas.